Staff: Mentor

3. The attempt at a solution
I know how to do the stress transformation, but my only issue is noticing why σ(x)= 0, I cant see it, can someone help me.

I assume that x is the thickness direction. Is that correct? If so, then the stress in the x direction is zero, because both surfaces of the pipe are in contact with the air (and the wall thickness is small compared to the lateral dimensions of the pipe).